The invention relates to a method for the recovery of sediments from the bottom of the sea by means of a freely suspended suction pipe provided at one end with a suction head which is slowly lowered into the sediment, while loosening means attached to the suction head are being kept in motion to dislodge the sediment.
The invention further relates to a device for carrying out the method, comprising a floating body from which the suction pipe is suspended which carries at its lower end the suction head having attached thereto the loosening means to dislodge the sediment to be recovered.
A prior art conveyor apparatus is known from German patent specification DE-OS No. 2 707 899, which includes a conveyor pipe, the lower end of which is movable and tightly fitting along its circumference into a cylindrical structure. Disposed between the cylinder and the end of the conveyor pipe is a drive means to reciprocate the two components in an opposed motion. This reciprocating motion not only serves to produce a pumping action, but also produces high frequency vibrations. Such vibrations are intended to assist in the penetration of the mud to be conveyed and to prevent the creation of channels therein. This object, however, is achieved only partially in actual practice.
The same disadvantage has been found in the conveyor device according to the earlier German patent specification P 28 41 203.5 in which vibrations are produced in a similar fashion as in the afore-mentioned well known device to loosen bottom formations. The vibratory movements are performed by a vibratory screen which may be in the shape of a cone pointing downward so that the direction of vibration is vertical. A device of this type is not capable of successfully loosening and dislodging relatively compact formations of a mud-like consistency from the sea bottom as they occur, for example, in the Red Sea at great depths. In any event, a device of this type is not capable of adequately loosening and dislodging sediment at any great depths in the sediment layers, but only near the less compacted surface where the sediment is of a sufficient fluidity.
It is the object of the present invention to provide a method for the recovery of sediments by means of a freely suspended suction pipe by which sediments having the consistency of compacted mud can be recovered easily and effectively from sediment layers of considerable depths.
This object is achieved by the method of the invention according to which the motion of loosening means is generated by the motion of the suction pipe. This has the great advantage that the free hanging suction pipe itself is directly utilized for the transfer of energy required to operate the loosening means so that no additional outside energy in the form of hydraulic powered lines or electrical cables is necessary. Moreover, no complicated drive motors need be provided on the suction head.
The principal premise of the present invention can be practiced in at least two different ways: first, by rotating the suction pipe on its upper end and, second, by continuously moving the suction pipe up and down. These two degrees of motion may also be scheduled to overlap. The heavy weight of the freely suspended suction pipe prevents great speeds, but the forces available to be transmitted to the lower end of the suction pipe are considerable. When lowering the suction pipe, the weight of it combined with the weight of the elements attached thereto, such as the suction head or the like, may be utilized to operate loosening tools as, for instance, scrapers or the like, which can scrape along the surface of a steep bank to loosen the material to be recovered. In similar fashion, great forces may be taken advantage of as the suction pipe is raised.
In order to generate a lateral reaction force by the loosening means upon a bank, the upper end of the suction pipe is constantly advanced toward one side so that the entire pipe assembly hangs tilted as at an oblique angle, and its weight, or the weight of the suction head, generates the force by which the loosening means are thrust against the bank to cut into the sediment along the edge of the bank.
Where rotary motion is employed to operate the suction pipe, the situation is similar. However, the rotary motion also produces forces in the direction of the continuous movement of the suction pipe which are transverse to the desired feed direction so that, in addition, a lateral sag is produced.
A device for carrying out the method of the invention includes a flexible suspension means on a floating body which may include a pivot bearing, with a rotary drive means being provided for rotating the suction pipe. Another embodiment of flexible suspension includes a vertically operating hydraulic device having a gas pressure storage container for compensating the weight of the suction pipe so that a drive means merely needs to generate the power to operate the loosening tools.
In the embodiment of the invention employing a vertical up and down movement, the preferred loosening means consists of blades, scrapers, or the like, because the required forces are within reasonable limits and the material fragments stripped from the sediment are of a rather uniform size and shape which is conducive to an efficient suction and conveying operation.
The stripping or scaling edges may be provided on hinged pivot plates which open up only in one direction of movement to effect the stripping, while folding down in the other direction of movement, thereby constituting a low degree of frictional resistance. However, depending on the character of the sediment, it may be of advantage to employ twin pivot plates which are operative in both directions of movement. In addition, the pivot plates may be provided with screens which project from the pivot plates into the interior of the suction head, that is, they follow the movement of the pivot plates. This has the result that rocky or lumpy material accumulating on the outside of the screen falls off.
As previously mentioned, the reaction forces may be generated by inducing a lateral sag of the suction pipe. It has also been found to be advantageous to provide a nozzle at the suction pipe above and/or on the suction head itself. The nozzle is connected with a water pressure source and is directed transversely to the direction of the suction pipe and facing away from it so as that the desired reaction forces are produced by recoil action. The direction of the forward thrust may be determined by an appropriate rotational movement of the pipe. This, however, may be difficult with large lengths of the free hanging suction pipe. For this reason it is preferred to provide mechanical guide means in the form of guide plates by which the suction head is guided in the trench.